1. Field of the Invention
The present invention relates to implantable medical devices and methods, and more particularly to a rate-responsive pacemaker and the manner in which such pacemaker is programmed in order to provide an optimum response for a particular patient.
A rate-responsive pacemaker is one wherein the pacing rate of the pacemaker (where the "pacing rate" is the rate at which the pacemaker provides stimulation pulses on demand) is adjusted automatically as a function of a sensed parameter. The parameter is measured by a sensor that may be included within the pacemaker or coupled to the pacemaker.
A common type of sensor used in rate-responsive pacemakers is an activity sensor that senses the physical activity level of the patient. Other types of sensors are also known, such as sensors that sense the blood oxygen level, the blood temperature, the blood pH, the respiration rate, or other parameters that indicate the need for a patient's heart to beat at a faster or slower rate.
The output signal from the sensor of a rate-responsive pacemaker is generally referred to as the "raw signal," or sometimes the "raw sensor input signal." The raw signal is processed in a prescribed manner by appropriate sensor processing circuits within the pacemaker in order to generate a sensor indicated rate (SIR) signal. The SIR signal, in turn, is utilized by the pacemaker processing circuits in order to define the pacing rate. Sometimes, the raw signal may be referred to as the "sensor input signal" (because it is the signal that is input into the sensor processing circuits of the pacemaker).
The manner in which the raw signal is processed by the sensor processing circuits is controlled by a plurality of sensor control parameters. Such control parameters define, for example, a threshold level above which the raw signal must reach before it is considered significant by the sensor processing circuits. Such parameters also define minimum and maximum SIR signals that define the lower and upper limits that the SIR signal may assume regardless of wide fluctuations in the raw signal, as well as the specific relationship that defines how the raw signal is converted to a specific SIR signal for values between the minimum and maximum SIR signals. The sensor control parameters may be fixed within the pacemaker or, as is more likely, may be programmed to desired values. Allowing the sensor control parameters to be programmed provides the physician with a technique for customizing the operation of a rate-responsive pacemaker for a particular patient.
For a more complete description of the general operation of a rate-responsive pacemaker, including the manner of programming such a pacemaker, and the typical sensor control parameters that may be utilized therein, reference is made to U.S. Pat. Nos. 4,712,555; 4,809,697; 4,940,052 and 4,940,053; which patents are incorporated herein by reference.
Disadvantageously, due to the number and interrelationship of sensor control parameters used in a modern rate-responsive pacemaker, the process of optimally programming such a pacemaker for a particular patient has become increasingly complex and difficult. The actual programming itself is not difficult nor complex, as modern programming aids, such as the analyzer-programmer system (APS), manufactured by Siemens Pacesetter, Inc. of Sylmar, Calif., have made programming any desired parameter into an implanted, programmable rate-responsive pacemaker as simple as following a sequence of menu screens displayed on the APS. The complexity and difficulty arises in knowing just what set of control parameters should be programmed for a particular patient in order to provide the most effective therapy. Such programming has become especially difficult as rate-responsive pacemakers have become more autonomic, controlled by inputs received from a multiplicity of internal sensors. What is needed, therefore, is a technique that assists a physician, or other medical personnel, in selecting an optimum set of sensor control parameters that may be programmed in a rate-responsive pacemaker.
A significant factor that makes the programming of a rate-responsive pacemaker so difficult is the variation in the sensor inputs from patient to patient. To appropriately program a rate-responsive pacemaker, a physician must anticipate how the pacemaker will respond in all conditions and activities that the patient is expected to exhibit. Because the physician, or other medical personnel, will not normally have sufficient information on which such programming decisions can be based, there is therefore a need for a tool or aid to assist the physician in anticipating the resultant pacemaker operation for each patient in activities that the particular patient will normally experience.
It is known in the art, as described, e.g., in U.S. Pat. No. 4,940,052, to collect SIR histogram data during the operation of a rate-responsive pacemaker, and to use such SIR histogram data as an aid to help program the sensor control parameters to appropriate values. However, such technique still requires gathering the SIR Histogram data, analyzing the SIR Histogram data to determine if the sensor control parameters are appropriately programmed, estimating how much the sensor control parameters should be changed, changing the sensor control parameters, re-gathering new SIR Histogram data based on the newly programmed sensor control parameters, and then re-analyzing the SIR Histogram data to determine if the sensor control parameters have been changed an appropriate amount. This process is repeated over and over again until the physician is convinced that the SIR Histogram data reflects an appropriate programming of the sensor control parameters. Unfortunately, such process typically requires several iterations, and is therefore very time consuming. Moreover, the process still involves a significant amount of guess work, or trial-and-error, in order to zero in on an optimum setting of the sensor control parameters. What is needed, therefore, is an improved technique for using the SIR Histogram data that simplifies and shortens the programming process, and minimizes the trial-and-error (guesswork) that has previously accompanied sensor parameter programming.
The present invention advantageously addresses the above and other needs.